[FFmpeg-devel] [PATCH] ffmpeg: Add option to force a specific decode format

[Mark Thompson]

Fixes #7519.
---
I've had this lying around for a bit with intent to use it to support non-hwaccel hardware decoders (in particular, v4l2m2m), but it actually fixes the force-hwaccel use-case too in a sensible way.


 doc/ffmpeg.texi      | 12 ++++++++++++
 fftools/ffmpeg.c     |  4 ++++
 fftools/ffmpeg.h     |  4 ++++
 fftools/ffmpeg_opt.c | 15 +++++++++++++++
 4 files changed, 35 insertions(+)

diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index 3717f22d42..9f9e693898 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -920,6 +920,18 @@ would be more efficient.
 When doing stream copy, copy also non-key frames found at the
 beginning.
 
+ at item -decode_format[:@var{stream_specifier}] @var{pixfmt} (@emph{input,per-stream})
+Set the output format to be used by the decoder for this stream.  If the
+decoder does not natively support this format for the input stream then
+decoding will fail rather than continuing with a different format.
+
+In general this should not be set - the decoder will select an output
+format based on the input stream parameters and available components, and
+that will be automatically converted to whatever the output requires.  It
+may be useful to force a hardware decoder supporting output in multiple
+different memory types to pick the desired one, or to ensure that a
+hardware decoder is used when software fallback is also available.
+
 @item -init_hw_device @var{type}[=@var{name}][:@var{device}[, at var{key=value}...]]
 Initialise a new hardware device of type @var{type} called @var{name}, using the
 given device parameters.
diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index 38c21e944a..73bed55e4d 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -2800,6 +2800,10 @@ static enum AVPixelFormat get_format(AVCodecContext *s, const enum AVPixelFormat
         const AVCodecHWConfig  *config = NULL;
         int i;
 
+        if (ist->decode_format != AV_PIX_FMT_NONE &&
+            ist->decode_format != *p)
+            continue;
+
         if (!(desc->flags & AV_PIX_FMT_FLAG_HWACCEL))
             break;
 
diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
index eb1eaf6363..88e0aa60ea 100644
--- a/fftools/ffmpeg.h
+++ b/fftools/ffmpeg.h
@@ -125,6 +125,8 @@ typedef struct OptionsContext {
     int        nb_ts_scale;
     SpecifierOpt *dump_attachment;
     int        nb_dump_attachment;
+    SpecifierOpt *decode_formats;
+    int        nb_decode_formats;
     SpecifierOpt *hwaccels;
     int        nb_hwaccels;
     SpecifierOpt *hwaccel_devices;
@@ -334,6 +336,8 @@ typedef struct InputStream {
     int top_field_first;
     int guess_layout_max;
 
+    enum AVPixelFormat decode_format;
+
     int autorotate;
 
     int fix_sub_duration;
diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
index d4851a2cd8..0e3e8b99fe 100644
--- a/fftools/ffmpeg_opt.c
+++ b/fftools/ffmpeg_opt.c
@@ -701,6 +701,7 @@ static void add_input_streams(OptionsContext *o, AVFormatContext *ic)
         AVStream *st = ic->streams[i];
         AVCodecParameters *par = st->codecpar;
         InputStream *ist = av_mallocz(sizeof(*ist));
+        char *decode_format = NULL;
         char *framerate = NULL, *hwaccel_device = NULL;
         const char *hwaccel = NULL;
         char *hwaccel_output_format = NULL;
@@ -797,6 +798,17 @@ static void add_input_streams(OptionsContext *o, AVFormatContext *ic)
             ist->top_field_first = -1;
             MATCH_PER_STREAM_OPT(top_field_first, i, ist->top_field_first, ic, st);
 
+            MATCH_PER_STREAM_OPT(decode_formats, str, decode_format, ic, st);
+            if (decode_format) {
+                ist->decode_format = av_get_pix_fmt(decode_format);
+                if (ist->decode_format == AV_PIX_FMT_NONE) {
+                    av_log(NULL, AV_LOG_FATAL, "Unrecognised decode format: %s",
+                           decode_format);
+                }
+            } else {
+                ist->decode_format = AV_PIX_FMT_NONE;
+            }
+
             MATCH_PER_STREAM_OPT(hwaccels, str, hwaccel, ic, st);
             if (hwaccel) {
                 // The NVDEC hwaccels use a CUDA device, so remap the name here.
@@ -3583,6 +3595,9 @@ const OptionDef options[] = {
         "audio bitrate (please use -b:a)", "bitrate" },
     { "b",            OPT_VIDEO | HAS_ARG | OPT_PERFILE | OPT_OUTPUT,            { .func_arg = opt_bitrate },
         "video bitrate (please use -b:v)", "bitrate" },
+    { "decode_format",  OPT_VIDEO | OPT_STRING | HAS_ARG | OPT_EXPERT |
+                        OPT_SPEC | OPT_INPUT,                                    { .off = OFFSET(decode_formats) },
+        "set output format used by decoder, fail if this format is not available", "format" },
     { "hwaccel",          OPT_VIDEO | OPT_STRING | HAS_ARG | OPT_EXPERT |
                           OPT_SPEC | OPT_INPUT,                                  { .off = OFFSET(hwaccels) },
         "use HW accelerated decoding", "hwaccel name" },
-- 
2.19.1